1. Field of the Invention
The present invention relates to tools for positioning and stretching carpet in the installation of wall-to-wall carpeting, and more particularly to a portable, impact-operated positioning and stretching tool.
2. Description of Related Art
In the installation of wall-to-wall carpeting, the carpet material is often attached to the floor to be covered around the periphery of the floor area, such as adjacent to the walls of a room. Thin, narrow strips of wood or like material having a plurality of sharp tacks protruding therefrom, referred to as xe2x80x9ctack stripsxe2x80x9d, are typically fastened to the periphery of the floor for this purpose. The carpet material is then temporarily attached to the tack strips along one edge of the floor area, stretched across the floor, and attached to the tack strips along an opposite edge of the floor area. The process is repeated with any remaining unattached edges of the carpet, until the carpet has been positioned and stretched as desired. The carpet may then be more permanently attached to the floor by flattening the tacks in the tack strip using a suitable hammering or flattening tool.
Various tools are used in the construction trade for stretching and positioning carpet onto the tack strips. One type of tool is exemplified by the relatively large, lever-activated stretching tools referred to as xe2x80x9cpower stretchers.xe2x80x9d Power stretchers typically comprise an extensible tube with a leveraged extension mechanism, a carpet engaging head at a first end of the tube, and a suitable pressure plate at the other end of the tube. The pressure plate is placed against a wall or other suitable stationary structure, and the tube is placed along the carpet material in the desired direction of stretch. The engaging head is engaged with the carpet, and the tube is extended a desired amount using the lever mechanism. As their name suggests, power stretchers are particularly useful for imparting a large amount of stretch to carpet. However, they are relatively large and may not be suitable for odd-shaped floor areas or for working in tight spaces.
Another popular type of tool in the trade is exemplified by the portable, impact-operated stretching and positioning tools referred to as xe2x80x9ckickers.xe2x80x9d Kickers typically comprise a relatively short extendable shaft (less than three feet, and more typically, about eighteen inches long) with a carpet engaging head on one end and a cushioned pad on the opposite end. Kickers are operated by impacting the cushioned pad while the engaging head is engaged in the carpet. An installer typically kneels astride the kicker and impacts the cushioned pad using the thigh and/or knee of one leg, while positioning the engaging head between strokes as desired. Using a kicker, a skilled installer can very quickly work around the periphery of a room or other area to be carpeted, sliding and/or stretching the carpet and fastening it to the tack strips. Being relatively small and versatile, kickers are especially preferred for use in tight spaces, with odd-shaped carpet areas, or for finishing work.
Although kickers remain an essential and popular tool of the trade, excessive or improper use of a kicker may lead to fatigue, back pain, or even back injury. If a kicker is struck too hard by a user""s knee, or is not positioned properly on the carpet, the shock of the blow may not be fully absorbed by the carpet that is being positioned by the kicker, and instead, a substantial portion of the shock may be absorbed by the user""s body. Over time, repeated use of a kicker may therefore cause or contribute to muscle or joint pain in users who use a kicker frequently, especially those who operate kickers using hard and forceful kicks. Discomfort and injury may be prevented by minimizing kicker use (for example, by using power stretchers instead of kickers whenever possible) and avoiding kicking a kicker harder than is needed to position the carpet. Despite these potential problems, however, many users prefer the speed and convenience of kickers over alternative methods. Many users also find it difficult to attenuate the force of their kicks so they are not overpowering the kicker.
One solution to the problems of shock loading associated with kickers is to provide a kicker that absorbs excessive shock from a kick, i.e., shock that is not absorbed by the carpet itself. Prior art attempts to provide kickers that absorbed the shock of user""s kicks have proven unsatisfactory, and have not been widely adopted by the trade. Instead, the vast majority of those in the trade use kickers without any shock-absorbing device, except for a cushioned striking pad that is relatively firm and provides a minimal amount of shock absorption. The limitations of prior-art shock-absorbing kickers are as follows.
In one prior-art, spring-cushioned kicker, the kicker shaft is configured in two parts, a tubular portion, and a solid, piston-like portion slideably engaged in the tubular portion. A coil compression spring is housed within a tubular portion of the kicker shaft, and disposed against the sliding shaft. The force of a kick is transmitted through and partially absorbed by the compression spring. However, this design suffers from several disadvantages. A compression spring that is xe2x80x9csoftxe2x80x9d enough to absorb substantial shock energy from a user""s kick, i.e., a spring with a low enough spring constant xe2x80x9ck,xe2x80x9d will also dramatically reduce the peak force delivered by the kicker to the carpet. The user will therefore expend a great deal of energy compressing the spring, and relatively little energy from the kicking stroke is available for moving the carpet. On the other hand, if a stiffer spring is used, the shock-absorbing property of the kicker is essentially lost. The stiffness of the spring is not adjustable, so even if a spring of optimal stiffness is used, the kicker is not uniformly useful with different types of carpets and for different users.
In another prior-art kicker, the function of the coil compression spring is performed by a sealed air cylinder that functioned as a gas spring. The length of the kicker connecting shaft is adjusted by increasing or decreasing the amount of air in the cylinder, which is therefore at atmospheric pressure when the kicker is at rest. When kicked, the air cylinder functions essentially like the compression spring of the spring-cushioned kicker, that is, to absorb the shock of impact and transmit the kicking force to the engaging head of the kicker. Therefore, the air-cushioned kicker suffers from the same disadvantages of the spring-cushioned kicker: the spring will absorb too much of the force of each kick, making the kicker harder to use, and the effective spring constant (stiffness) of the air cylinder is not adjustable.
It is desired, therefore, to provide a shock-absorbing carpet kicker that overcomes the limitations of prior-art shock-absorbing kickers. The shock-absorbing kicker should be affordable, easy to use, and should not present any significant disadvantages with respect to an ordinary kicker, while helping to prevent injuries associated with excessive or improper use of conventional kickers.
The present invention provides a shock-absorbing carpet kicker that overcomes the limitations of prior-art kickers. The kicker of the invention may be constructed cost-effectively, and may be made as versatile and easy to use as carpet kickers that are in use today. At the same time, the kicker is expected to substantially reduce shock and stress on the user, and enhance users"" comfort during use.
The carpet kicker may comprise many elements in common with conventional kickers. A structure including a carpet-engaging head connected to a cushioned impact pad via an adjustable shaft may be used, such as may be found in conventional kickers. In addition, a pre-loaded shock-absorbing device is interposed between the cushioned impact pad and the engaging head, at any suitable location along the adjustable connecting shaft. The shock-absorbing device is connected to the other structural elements of the kicker so as to transmit and/or absorb substantially all of (preferably, all of) the energy of each kick by the user. That is, the portion of the energy of each kick that is not absorbed by the shock-absorbing device is substantially transmitted (and preferably, entirely transmitted) to the engaging head.
The shock-absorbing device has a specific configuration, as follows. Conceptually, the shock absorber comprises a resilient member, such as a mechanical spring, configured to absorb energy from a blow to the cushioned pad directed towards the engagement head. The resilient member is mounted in parallel to, and preloaded against, a collapsible tension member. For example, the resilient member may be a compression spring, although other types of springs may also be used, such as a tension spring, provided the other elements of the shock-absorbing device are suitably rearranged. Furthermore, the resilient member is not limited to mechanical springs, but other resilient devices, such as gas springs, may also be used. The collapsible tension member is a mechanism or device, such as a flexible cable, a piston/cylinder assembly, or a mechanical linkage, that is relatively strong and rigid when fully extended under a tension load, and which will collapse under a relatively low compressive load.
The resilient member is pre-loaded against the collapsible member, maintaining it in tension when the kicker is at rest. Because of the pre-load, the resilient member will not immediately compress under the compressive force of the kick. Instead, the shock-absorbing device will remain rigid until the pre-load force is exceeded by the force of the kick. Therefore, most of the initial energy of the kick will be transmitted to the engaging head. Only if and after the force of the kick exceeds a certain level will substantial energy be absorbed by the resilient member.
The amount of pre-load is preferably adjustable by the user of the kicker, such as by turning an adjustment knob on the connecting shaft. An adjustment knob, or other suitable mechanism, may operate by moving the resilient member relative to the collapsible tension member. Preload may be increased by moving the resilient member so as to increase the compression of the resilient member, and decreased by movement in an opposite direction. Such adjustability provides users with the ability to tune the response of the kicker for use with different types of carpets and for individual users"" kicking styles.
Advantageously, the collapsible tension member may be a damping device, such as a gas cylinder configured for damping motion. The damping qualities of such a device provide the additional advantage of reducing the backlash of the resilient member. In addition, a damping device may also absorb excess energy during compression of the resilient member, thereby reducing energy dissipation and heating of the resilient member. The damping qualities of a damping device for use in the kicker may also be adjustable by users, such as through adjustment of a gas bleed valve. A damping adjustment may provide users with another way to adjust the dynamic response of the kicker for various use conditions. The damping device may be configured to provide two-way damping (damping in both directions of the cylinder stroke) or one way damping (damping in a single stroke direction and undamped in the opposite direction).
In an embodiment of the invention, the shock-absorbing device comprises a coil compression spring disposed on the outside of a cylindrical gas damping device. The coil spring is compressed between an adjustment knob on the cylinder housing and a retention washer on the piston shaft near an opposite end of the damping device. The coil spring thereby causes the piston of the damping device to be fully extended when at rest. The adjustment knob is threaded onto the cylinder housing, whereby the extent of preload of the coil spring may be adjusted by turning the knob. The shock-absorbing device is preferably a relatively small modular unit that may readily be mounted in-line with the connecting shaft of a conventional kicker. Thus, a kicker may be constructed according the invention at an affordable cost.
A more complete understanding of the shock-absorbing carpet kicker will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly.